1. Field of the Invention
The present invention relates to an alarm system for preventing loss or theft of one or more articles. More particularly the system of the invention can be used in preventing loss of wallets or other valuable personal articles, as well as in the surveillance of items that can be moved, e.g. for being used, but not taken away, as it happens for example in respect of government or notary's seals.
2. Description of Related Art
From EP-A-0 139 698 it is known a reminder alarm system for preventing loss of articles which provides several emitters transmitting signals to a receiver/alarm sounder, with each emitter triggering the alarm signal as soon as the signal from it goes below a predetermined level, depending on the distance therebetween.
U.S. Pat. No. 4,843,371 discloses a burglar alarm system comprising a portable wireless transmitter and a receiver mounted in a briefcase forming a distance-measuring device which triggers an alarm when the distance between the receiver and the transmitter exceeds the receiving range.
Anti-theft systems providing a tag attached to an article to be protected are also known, see for example EP-A-0 494 409.
A drawback of the known devices is that they do not provide reliable protection of both a single article and a plurality of articles with the same device.
Moreover the known systems used for protecting articles within a fixed area, such as articles in a wholesale store, cannot be used as a portable alarm system to be worn by a person for warning him of a theft, or as a simple reminder in case of inadvertent oversight.
On the other hand the known systems for preventing loss of portable articles and the anti-theft devices are unsuitable for protecting objects that are to be confined--and in case used--in a fixed area, such as seals in a notary's office.
Additional drawbacks of the known systems are that the power consumption of the tags or devices attached to the articles to be protected is not negligible and therefore the useful life of such tags is rather short.
Moreover in the known systems the range of protection cannot be adjusted, and the environment often renders unreliable their working.
The object of the present invention is to overcome the above mentioned limitations and shortcomings, and more particularly to provide a system that allows the simultaneous protection of a number of articles with an extremely low power consumption of the devices attached to the protected objects so that the protection is reliably ensured for a long time.
Moreover the invention aims to realize a system that is really flexible so that the same arrangement can be used for protecting a single article as well as a plurality of articles, or as an alarm system for preventing the loss or theft of one or more personal objects such as a wallet. This renders the system of the invention both inexpensive and reliable.